Electric cooking stove and the like



2a 24 Ag I I I I I r I 1 x I r W. H, MYERS Filed Feb. 19, 1931 ELECTRIC COOKING STOVE AND THE LIKE May 7, 1935.

veN1'aK flab cuits.

Patented May I, 1935 UNITED STATES ELECTRIC COOKING Walter STOVEANDTHELIKE Harold Myers, Wollstonecraft, New

South wa Animus Application February 19, 1931, Serial No. 517,055 In Australia June 2, 1930 2Claims.

This invention relates to electrically heated cooking stoves and like devices, but more especially refers to apparatus of this type which is designed to operate on alternating current cir- The object of the invention is to provide, primarily, a stove or the like in which the current for obtaining the necessary heat is supplied at a voltage which is sufllciently low to avoid all possibility of perceptible or dangerous shock and in which a supply of hot water will be permanently available, the losses created in the transformer or equivalent device employed for providing the necessary low voltage current being utilized to heat the supply of water. A further object is to provide a stove which shall be. of rigid, simple and economical construction and which shall have long life and operate eillciently. Further objects of the invention are to provide a stove in which heating elements of large section and open construction will rapidly reach the desired temperature and will convey the heat rapidly by convection and radiation to the utensils irrespective of their shape and in which simple, rapid and effective methods of adjusting the heat of the elements are provided. Still further objects and advantages of the invention will be apparent from the following description of the invention in which reference will bemade to the accompanying' explanatory drawing, in which Figure 1 is a diagrammatic partly sectional perspective view of a form of stove constructed according to the invention and Figure 2 is acircuit diagram of the electrical connections.

According to the invention there is provided a water tank 3, an oven structure 4 and a cooking.

table 5. The various parts are arranged as may be found most convenient. For example, as illustrated, the water tank may be placed below the oven, while the cooking table 5 is bolted.

or otherwise secured to a main frame 6 retaining the other parts, the table being supported as a cantilever.

The water tank 3 is lagged on every side and at the top and bottom and has located within it at a relatively low point, as within the wall I, a

transformer 8 of a capacity suitable for the requirements of the installation. 7

The transformer is of. well known type and may or may not be'cased as at H, but it is preferably wound with heatresisting windings. If it is not cased'and the core with its windings are immersed in direct contact withthe water, suitable treatment for withstanding the eifects of immersion and preventing .corrosionwill be applied. If it is cased the casing material is preferably of Monel metal or other ,non-corroding materiaL- The transformer I may be provided with tappings 9 on the high voltage side ID in order to compensate for varying voltages of supply, thus providing both a means of keeping the elements at the right temperature and also of obviating-the necessity for the supply authority to add to a feeder system prematurely. The primary high voltage leads 3| are taken to the transformer through a pipe 32 which projects through the cover of the water tank or are led to the winding in any other well known manner whichwill ensure a water tight connection. The secondary leads 20, 25 and 26- are also conveyed from their winding through a similar pipe 33 or in any other well known and watertight manner.

The tank is provided with appropriate and well known outlet means I2 and inlet means (not shown in the drawing), a gauge glass it, a thermometer, if required and, if considered necessary, with any well known means such as a ball operated valve for ensuring that the water level will not fall below the top of the transformer structure. The transformer 8 is designed to produce from its secondary IS an output current of relatively low voltage, preferably in the vicinity of 35 volts, from the supply voltage and one side of the secondary winding I is earthed as at it to the tank structure or if the tank is included within the other parts, to the frame containing them.

The cooking table 5 is formed from suitable material such as cast iron or the like and is attached to the other parts so that it is mechanically rigid, butso that it is electrically insulated as at II from them if the secondary winding II of the transformer 0 is earthed to the main frame.

The cooking table heating elements l8 are arranged to drop into slots or recesses formed in the cooking table 5 and may be of any suitable well known type but preferably consist of a metal ring having a number of radial arms converging towards the centre. These arms are adapted to receive blocks of refractory insulating material grooved or otherwise shaped so that when they are clamped to the arms they will retain in a rigid manner the heating element beneath the arms and which is wound in a spiral or other form of a heavy gauge resistance wire or strip of any suitable and well .known material. One end of the spiral is taken to a knife contact blade I! which is attached to the ring structure-so that it is insulated from it. This blade is adapted to enter a spring contact or the like mounted towards the rear side of the cooking table and connected electrically to a busbar 20 or other electricalconnection which, together with the spring contact is insulated from the cooking table 5 and which is adapted to enter a spring contact mounted on, but insulated from, the frame structure towards the front side of the cooking table. A flexible connection 22 is taken from this contact to a switch blade 23 mounted upon a shaft rotatably mounted so that the blade may make selective contact with one, two or more spring contacts 25. If one contact only is provided it is connected to a. busbar 25 which is connected to the unearthed side of the secondary I5 of the transformer. The additional contacts if provided are connected to busbars 26 which are led to tappings 21 in the transformer secondary l5. Thus, by manipulating the switch blade 23, connection may be made to suitable tappings in the secondary transformer winding so that the voltage and hence the heat of the element may be regulated as desired.

The heating regulation may alternatively or in addition be obtained easily and cheaply by including in series with the element an adjustable reactor with or without a moving core of iron wire, the constituent parts of which may be embedded in cement to maintain them in position and prevent hum. The adjustable reactor may-be replaced by a variable rheostat either of the type consisting of a sliding arm moving over a resistance winding or of the type employing carbon plates to which varying pressures may be applied. The reactor is of advantage in that only a small amount of energy is wasted in the regulation. Any of the regulating means described above have the advantage that the heating of the element is regulated as a whole and in a uniform manner without the necessity for tappings on the element itself.

Accidental short circuiting between successive turns of the element can cause no harm because of the low voltage used and the insulating value of the oxide formed on the metal of the element and thus the element can be made in an open construction so that immediately energy is sup plied it may be transferred by radiation and contraction to the cooking utensil which may have an irregular surface without aflecting the efliciency of the heat transfer. Conversely, for the cooking operation known as simmering this form of element has a marked advantage in that the temperature is very rapidly reduced by switching on to the lower voltage busbar.

The oven 4 is also provided with heating ele-' ments of the open type previously described, similar heat regulating means being provided, the frame of the oven heating element being insulated from earth and the transformer and tank casing, in the event of the oven structure itself not being so'insulated. The oven elements, which for the purpose of illustration are indicated at 34, are preferably so constructed that they may be plugged in any well known manner at the points 35, current being conveyed thereto by the leads 36 and the heat control being effected by switches 23 or in the alternative manner indicated above. There may be one, two or more elements according to the size of the oven or the degree of heat required.

The water in the tank 3 is warmed by the heat losses in the windings and core of the transformer 8 when it is connected to the supply system and as such heat is not wasted the design of the transformer need not be generous so that considerable saving in its construction may be eflected. The water in the tank provides heat for the oven 4 or for any part of the structure overlying it. The tank and transformer may be mounted separately from the oven and/ or cooking table in which case suitable low voltage connections are made to the oven and/or cooking table.

A booster element 28 preferably connected to the low voltage winding of the transformer may be provided within the water space 28 of the tank 3 if water of a greater heat or in a-greater quantity is desired, suitable connections being made to produce the necessary heating effect. The heat regulation of the booster element-28 may beeffected by means of a switch 23 operated in the manner described above or in any other suitable and well known manner. One or more voltage power points 30 may be connected to the secondary I 5 for the purpose of utilizing other electrical apparatus such as irons and the like of suitable voltage, any of the heat regulating dew'ces previously described being inserted in the circuits to these points so that the heating of such appliances may be nicely adjusted; 'One form of heat regulation suitable would be a switch 23 adapted to make contact with either the full voltage busbar 25 or to one or more loweryoltage busbars 26.

The usual protections, such as earthing of the transformer, core and such parts of the frame of the apparatus as can be earthed, may be taken to prevent accident in the case of a failure of the primary winding of the circuit thereon. The power supply to the primary winding is controlled in any well known manner.

Throughout the specification reference has been made to a transformer for supplying current at the required voltage to the heating elements. It is to be clearly understood that the term transformer includes any suitable and well known device for achieving the same object, such as an auto-transformer or in the case of a multiphase circuit a transformer or transformers suitable for the circuit.

In the specification the secondary current is referred to as being supplied at a low voltage. It is to be understood that the voltage is not necessarily confined to the volts mentioned above, but it may be any voltage suitable for the purpose as long as it is not so high to render the use of open elements dangerous, or likely to cause perceptible shock. Preferably exceed volts.

I claim:

1. In an electric cooking stove provided with a heating device and having a supply circuit therefor, a transformer in the circuit, a water chamber forming part of the stove, and the transformer being located in the chamber below the normal water level for utilizing the heat of the transformer for heating the water a separate heating unit in said circuit and locatedin said chamber to heat the water to a higher temperature.

2. In an electric cooking stove provided with a heating device and having a supply circuit therefor, a transformer in the circuit, a water chamber forming part of the stove, and the transformer being located in the chamber below the normal water level for utilizing the heat of the transformer for heating the water and a water tight casing about the said transformer and made of non-corroding material.

WALTER mmom the voltage will not 

